Regulation of Jacobaea vulgaris by varied cutting and restoration measures

The growth of the noxious grassland weed Jacobaea vulgaris Gaertn. in pastures is a threat to grazing animals. This is especially true when it dominates vegetation cover, which often occurs on non-intensively used pastures that are managed for nature-conservation, to maintain and promote biodiversity. Thus, we wanted to find management techniques to reduce J. vulgaris without harming the floral biodiversity on the pastures. We tested six different mechanical and cultural methods to reduce the presence and spread of J. vulgaris. Seven study sites in Northern Germany (Schleswig-Holstein) were treated with tilling and seeding (1), tilling and hay transfer (2), mowing twice within bloom (3), mowing before seed set and combinations of mowing and seeding with a slit drill (5) or by hand (6). Our results show that cutting within the bloom of the plant at the end of June and again four weeks later, when the plant is in its second bloom was the only treatment leading to a significant reduction in population growth rate without reducing surrounding plant species richness. The study reveals that management of J. vulgaris in non-intensively used pastures is possible, while preserving species-rich grasslands.


Unfunded studies
Enter: The author(s) received no specific funding for this work.     North America, New Zealand, and Australia (1). As the plant's pyrrolizidine alkaloids pose a 34 health risk to cattle when consumed (2), the control of J. vulgaris is a primary management 35 goal of many farmers and in some countries even prescribed in their legislation (3). In intensive 36 grasslands, high fertilizer input, high cutting frequency, and chemical weed management 37 precludes the occurrence of J. vulgaris. It's control is challenging, though, in low input 38 grasslands that are managed for high plant and animal diversity, yet prone to massive J. vulgaris 39 spread (4). Taking this into account, we tested management strategies that aim at controlling J. 40 vulgaris without jeopardizing wild plant diversity.

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In order to increase the effectiveness of cutting in suppressing J. vulgaris, the frequency and 57 timing of cutting is essential because the proportion of nutrients and energy invested in different 58 plant parts varies among life-stages (16, 17). As J. vulgaris grows back quickly after cutting 59 (14), a second cut may be necessary before the second bloom. While this cutting regime may 60 prevent generative reproduction, it may induce vegetative reproduction, clonal growth or a 61 switch to a perennial life cycle (1). Since J. vulgaris usually dies off after seed production (18), 62 cutting before seed dispersal may be another option that may not only prevent vegetative re-63 growth but also seed dispersal.

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In addition to an adapted cutting regime, sowing other species can suppress weeds (19).  freshly cut, seed-containing biomass from species-rich grasslands (green hay) is another 74 effective method to restore grasslands (26). When green hay is transferred, disturbance to an 75 existing sward has been shown to enhance seedling establishment (27). Under high seed 76 pressure from J. vulgaris, however, sward disturbance will also enhance the weed's 77 establishment (9); thus, slot drilling and broadcast sowing without sward disturbance may be 78 promising techniques (28) to combine with the adapted cutting regimes to reduce establishment 79 and growth of J. vulgaris. Therefore, we also applied a combination of cutting regimes and

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The objective of our study was to find the optimal treatment, timing, and frequency for 89 grassland management on non-intensive pastures that leads to a maximal weed reduction and a 90 minimal loss of co-occurring vegetation. We studied six different management options for five 91 years. 92 We addressed the following research questions:    Table 1 Treatments found and collected in northeast Germany (see Table S2, Supporting Information) were sown 141 and rolled. For the biodiversity 2 treatment, freshly cut plant material was transferred from 142 species-rich donor-sites nearby. Thereafter, cattle were fenced out of the seed-enriched area 143 some weeks to allow seedling establishment. For the combination treatments, 1.5 g/m 2 of the 144 seed mixture mentioned above (see Table S2, Supporting Information) was sown by slit drill    The seven treatments led to three distinct response patterns (Fig. 3). Both biodiversity 221 treatments showed an initial decline in J. vulgaris abundance but a rebound after the fourth  The LTRE analysis showed that differences in the population growth rate (Δλ) between each 269 treatment and the control were mainly the result of differences in generative reproduction and 270 survival (Fig. 6). The analysis also demonstrates that the influence of vital rates on population 288 The seed addition in biodiversity and combination treatments led to species enrichment. About 289 five more plant species were found on plots with seed addition (biodiversity and combination) 290 compared to control plots. In the last year of the experiment only species richness in the 291 combination treatments was significantly higher than in the control treatment. All management 292 measures but the control enhanced species richness (Fig. 7). Richness patterns varied over the study period (Fig. 7)  (mean: three endangered species per one square meter vs. zero or one species in the control).

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Plants categorized as characteristic grassland species were most numerous in the biodiversity 1 312 treatment, followed by hay transfer (biodiversity 2) and combination treatments with mowing 313 and sowing (Fig. 8). Biodiversity treatments and the combination 2 treatment led to significantly 314 higher numbers of endangered plants than in the control. with seeding or plant material transfer, i.e. biodiversity 1 and 2, followed by combination 2, 323 which combined to sowing impulses and mowing (Fig. S3, Supporting Information). Turnover 324 rates of pure cutting treatments, combination 1, and the control were significantly lower and 325 did not differ from each other. The percentage of target species contributing to the turnover rate 326 was highest for biodiversity 1 (37 ± 0.02 %) and combination 2 (35 ± 0.03 %) and lower for 327 combination 1 (29 ± 0.02 %) even though these differences were not significant. The biodiversity treatments led to a drastic decrease in J. vulgaris abundance in the first two to 332 three years (Fig. 3). The decrease was especially pronounced, significant, and lasting in the 333 biodiversity 1 treatment for the flowering stage (Fig. 4). Although the general abundance sown plots compared to untreated plots in the four years after milling and sowing took place. 350 We assume that this is due to differences in the initial setting of the study by Bezemer et al.

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(2006) and our study. While in our study, grazed grassland was the control baseline, i.e. cattle

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The LTRE analysis showed that the population growth on milled sites was due to an increased 358 generative reproduction (Fig. 5)  found that plants defoliated by the butterfly Tyria jacobaeae die less than those setting seeds 390 probably due to higher resource investments involved in seed production than in regrowth.

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Cumulative effects of constant mowing regimes were also found by 55 (2014 rosettes. Yet, J. vulgaris population structure and growth rates were highly variable across 407 years, such that year had a stronger effect on population growth than management. We observed 408 an oscillating pattern with falling and rising J. vulgaris abundance every other year in seed cut, 409 combination, and control treatments (Fig. 3). Extreme weather conditions, such as  seed cut, and combination 2), in which more species were able to establish due to reduced 435 competition by dominant grasses (61). Diversity patterns of the treatments changed over time.

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Biodiversity treatments were most species rich in the first two years after milling and seeding 437 or green hay transfer. However, species numbers and cover of target species in biodiversity 438 treatments declined after the third year ( Fig. 7 -8). Other studies also showed that initially high 439 species numbers in sown treatments decreased after some years (50, 62, 63). One reason for 440 this decrease is that ruderal species and former arable weeds occur initially after milling and 441 vanish later on (27, 64). Therefore, species turnover was highest in mill-sow treatments 442 (biodiversity treatments 1 and 2) and seed-addition treatments (combination treatments 1 and 443 2), whereas turnover in the pure cutting treatments (flower and seed cut) did not differ from the 444 control.

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Species turnover in biodiversity and combination treatments led to a higher share of 446 characteristic grassland species. Percentage of characteristic grassland species was highest in 447 biodiversity and combination treatments (Fig. 8). As numerous other studies showed, without 448 bridging dispersal limitation by actively introducing seeds, it is rather unlikely that species-rich 449 grasslands will develop on former arable land (65; 66). This is due to the disappearance of 450 characteristic grassland species in intensively used agricultural landscapes (67). This is 451 especially problematic within modern agricultural landscapes in Northern Germany, which are 452 characterized by severe habitat fragmentation and biodiversity losses in grasslands (68).

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The percentage of characteristic grassland species in biodiversity treatments was approximately 454 40%, which was 10 % higher than in treatments without seed addition. While the number of Slight J. vulgaris decline occurred under all treatments and consequently we found no 477 significant differences in J. vulgaris abundance between the applied treatments and the control.

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Even the most effective treatment, the flower cut treatment, which was significant by trend and 479 the only treatment resulting in a population growth rate below one during the complete study 480 period, did not lead to a complete disappearance of J. vulgaris but allowed on average five 481